The present invention relates to the diagnosis and treatment of ailments such as cancer and, more particularly, to a method of stereotactic diagnosis and treatment with reference to an image of the target region of the patient that combines a high-resolution structural image such as a CT or MRI image with a lower resolution functional image such as a nuclear image.
Several diagnostic and therapeutic techniques that are used to diagnose or treat cancer involve the insertion of an instrument such as a needle, from outside the patient, into a tumor that is suspected of being cancerous. For example, a biopsy needle commonly is inserted into the tumor to withdraw a tissue sample for biopsy. In brachytherapy, a radioisotope is placed at the tip of a needle, and the tip of the needle is inserted into the tumor to deliver radiation to the tumor with minimal irradiation of the surrounding healthy tissue. Chemotherapeutic agents also may be injected into the tumor using a needle. The needles often are inserted into the patient with reference to a series of structural images of the patient, such as ultrasound images or CT images. These images are acquired before and during the insertion of the instrument, to verify that the instrument is being directed towards the correct target and is bypassing organs such as blood vessels which should not be penetrated by the instrument.
A tumor may include both cancerous tissue and non-cancerous tissue. It would be useful to be able to direct an instrument specifically to a cancerous portion of a tumor, and to avoid an obviously non-cancerous portion of a tumor. In the case of a biopsy, the needle should be directed towards the portion of the tumor that is most likely to be cancerous. In the case of brachytherapy, the needle should be directed towards the portion of the tumor that is known to be cancerous. Structural imaging modalities, such as CT and MRI, that have enough spatial accuracy and resolution to distinguish resolve tumors, are nevertheless unable to differentiate cancerous tissue from noncancerous tissue because they resolve only structure. Functional imaging modalities, including tomographic nuclear imaging modalities such as SPECT and PET, can distinguish cancerous tissue from noncancerous tissue but lack the spatial accuracy and resolution that is needed for the accurate positioning of instruments such as biopsy needles and brachytherapy needles.
It is known to register a functional image with a structural image to produce a combined image. See, for example, M. W. Vannier and D. E. Gayou, "Automated registration of multimodality images", Radiology, vol. 169 pp. 860-861 (1988); J. A. Correia, "Registration of nuclear medicine images, J. Nucl. Med., vol. 31 pp. 1227-1229 (1990); J-C Liehn, A. Loboguerrero, C. Perault and L. Demange, "superposition of computed tomography and single photon emission tomography immunoscinigraphic images in the pelvis: validation in patients with colorectal or ovarian carcinoma recurrence", Eur. J. Nucl. Med., vol. 19 pp. 186-194 (1992); F. Thomas et al., "Description of a prototype emission transmission computed tomography imaging system", J. Nucl. Med., vol. 33 pp. 1881-1887 (1992); D. A. Weber and M. Ivanovic, "Correlative image registration", Sem. Nucl. Med., vol. 24 pp. 311-323 (1994); and Hasegawa et al., U.S. Pat. No. 5,376,795. All six of these prior art documents are incorporated herein by reference for all purposes as if fully set forth herein. In principle, a sequence of such combined images could be used to direct an instrument to the cancerous portion of a tumor. In practice, the multiple imaging sessions and registrations that this would require make this solution impractical and possibly dangerous.
Stereotaxis is a known technique for localizing a region inside the body of a patient from outside the body of the patient, and for directing an instrument such as a needle, or a narrow beam of therapeutic radiation, to the target region. The degree of accuracy needed for stereotaxis is relatively high, so that the technique has been considered useful mainly on the brain and the breast. For example, in stereotactic radiosurgery of the brain, a CT localization frame is attached rigidly to the head of a patient and a CT image of the patient's brain is acquired with the CT localization frame in place. The position of the CT localization frame in the CT image is used to position the patient with respect to the source of the beam of radiation so that the beam intersects the desired target. Note that the CT localization frame is removed from the patient's head before the therapeutic irradiation commences.
There is thus a widely recognized need for, and it would be highly advantageous to have, a method of stereotactic diagnosis and therapy that could be used to direct a diagnostic or therapeutic instrument to a cancerous portion of a tumor located in a portion of a patient other than the patient's head or breast.